Photo/Illutration An ambulance parks next to the Diamond Princess cruise ship docked at Yokohama Port on Feb. 12. (Satoru Iizuka)

Coronavirus infections aboard the quarantined cruise ship Diamond Princess rose to 174 after 39 more people tested positive, the health ministry said Feb. 12. The infection also spread to a quarantine officer who helped to keep track of the health of crew and passengers.

An additional four passengers had developed severe symptoms, the ministry said.

To date, 492 crew and passengers of the nearly 3,700 people on board have been tested for the coronavirus. The vessel was placed under a minimum two-week quarantine on Feb. 5 and remains berthed at a pier at Yokohama Port.

Of the new cases, 10 were crew members and 29 were passengers, who ranged in age from their teens to their 80s, the ministry said. Ten of the infected passengers were Japanese, while seven were from the United States and four each from China, Australia and the Philippines.

Those who tested positive will be taken to local hospitals for medical treatment.

The male quarantine officer who tested positive boarded the ship on Feb. 3 and 4 to collect questionnaires and check for fevers. He followed protocol and wore a face mask and gloves while on the ship and sanitized his hands with disinfectant.

He worked at the quarantine office between Feb. 5 and 7 and developed a fever on Feb. 9. He went to a medical institution the following day where he tested positive for the coronavirus. Those who were in close contact with the quarantine officer, such as his family and colleagues, were urged to refrain from going outdoors.

Health ministry officials said four of the 135 crew and passengers who tested positive for the coronavirus by Feb. 10 had developed severe symptoms. The four were all male. One was in his 60s and the others were in their 70s. Three of them are Japanese. All four had pre-existing health problems and are now in an ICU using oxygen masks.

Based on this new development, health ministry officials are considering allowing senior citizens with pre-existing health conditions to leave the ship even if they display no symptoms of the coronavirus ahead of the scheduled Feb. 19 end to the quarantine period.

At a task force meeting to deal with the coronavirus on Feb. 12, Prime Minister Shinzo Abe indicated that local governments would be given greater leeway in deciding to test a wider range of people for the coronavirus.

The current standard is to test those who have been to Hubei province in central China, where Wuhan is located and the outbreak started.